Screw thread grinding attachment



Nov. 22, 1955 w. J. FENNELL SCREW THREAD GRINDING ATTACHMENT Filed April 9, 1952 Q6 Q2 l- INVENTOR H Z r m A F J m m l K 1 B 1 I W m L United States Patent Q l 2,724,223 SCREW THREAD GRINDING ATTACHMENT William J. Fennell, Havertown, Pa.

Application April 9, 1952, Serial No. 281,380

3 Claims. (Cl. 51-232) This invention relates to thread grinding devices, and

more particularly to a detachable thread grinding attachment for use with conventional surface grinders having magnetic chucks.

The grinding of screw threads is becoming more common, for the reason that: (1) grinding produces a more accurate thread both as to form and lead or pitch; (2) the surface produced is smoother, which feature is important in parts made of hardened steel, because hardening leaves a scale on otherwise preformed threads, and (3) grinding of the threads disturbs the internal or crystalline structure of the metal less than if the threads are cut on a lathe or are cut with a die, since with grinding there is no disruption or tearing of metal in the area contiguous to the screw thread, as is the case with both lathe or die cutting.

Conventional thread grinding machines are complicated and costly, and their use is generally restricted to establishments having a sufiicicnt volume of business to render their purchase economically desirable. Very few small machine shops can afford to install thread grindingv machines, because of the high initial cost, and because they usually do not have sufiicient work to keep such machines occupied. Accordingly, when small shops have work which requires ground threads, as on hardened steel, the work must be sent out to establishments having the necessary equipment, which is a most uneconomical procedure.

A standard piece of equipment for machine shops, even the small shops, is a magnetic chuck surface vgrinder. Surface grinding machines are well known in the art, and among the better known makes are those manufactured by Brown & Sharp, Reed Taft-Pierce, Grand Rapids, and other manufacturers. These machines are used to produce a fiat surface on metal work pieces byKgrind-ing. They all follow the same general patternin design, which consists of a suitable-frame supportingjthe' arbor for the grinding wheels, and ways for supporting a saddle on which the Work table rests. Mleans are provided for moving the work table and the saddle, as well as for elevating and lowering the grinding wheel arbor. Most of these machines are provided with a magnetic chuck,

which is clamped on the work table, and on these mag.

netic chucks the work pieces are held when grinding the surfaces. After considerable research and experimentation, I have discovered that the usual magnetic chuck surface grinder can be quickly converted to an efficient screw thread grinding machine by the use of an im-. proved work holding attachment which can. be detach- Ptented Nov. 22, 1955 2 novel work holding attachment for use with magnetic chuck surface grinders, whereby the grinders can be converted, at will, to screw thread grinders.

It is valso an object of my invention to provide a readily detachable work holding attachment for use with magnetic chuck surface grinders, whereby the surface grinders can be converted, at will, to screw thread grinders of any desired pitch, and without involving any structural alteration or dismantling of the surface grinders, or any parts thereof.

A further object of my invention is to provide a combination surface grinder and screw thread grinder, utilizing a conventional magnetic chuck surface grinder as the basic element.

Another object of my invention is to provide a reciproing as a detachable unit readily apposable to and detachable from a conventional magnetic chuck surface grinder.

It is also an object of my invention to provide a screw thread work holder of the character described with detachable master thread units, whereby a number of units of respectively different thread pit'ches 'are usable with a single work holder.

An additional object of my invention is to provide. a universal surface and screw thread grinder, utilizing a conventional magnetic chuck surface grinderas the basic element, and a detachable work holding attachment tov convert it to a screw thread grinder.

Yet another object of my invention is to provide screw thread work holder of the character described, reciprocable in a base member, the combination functioning as a detachable unit readily apposable to and tie tachable from a conventional surface grinder.

With these and other objects in view, which may be incident to my improvement, the invention 'consistsin the parts and combinations to be hereinafter set forth and claimed, with the understanding that the several necessary elements comprising my invention, may be varied in construction, proportions and arrangements without departing from the spirit and scope of the appended, claims.

In order to make my invention more-'clearlyunderstood, I have shown in the accompanying drawings means for carrying the same into practical effect, withoutlimiting. the improvements in their useful application to the particular constructions, which for the purpose of explanation, have been made the subject of illustration.

In the drawings, like numerals refer to similar parts;

throughout the several views,.'of which tachment;

Fig. 2 is a side elevation, partly in section, of a work holding attachment as apposed to the magnetic chuck of a surface grinder, the wheel of the grinder being shown in juxtaposition to the Work piece, and t Fig. 3 is an end elevation of the device showing the crank handle master screw control.

Referring to the drawings, and more particularly .to- Figs. 1 and 2, the novel screw thread grinding fixture is a two-part device comprised of a base lliand a reciproc-able work holder 20 incorporating a master thread unit 30. The base is adapted to be held in .a suitable chuck of a surface grinding machine, and inthe preferred form of the invention, as indicated hereinabove, the novel screw thread grinding fixture is used to convert a com ventional magnetic chuck surface grinder to a screw with particular reference to such use, it will be appreciated that mechanical hold-downs will be used with surface grinders which do not have magnetic chucks.

, The fixture base 10, which is desirably made of steel or other suitable magnetizable material, .comprises a bottom plate member 11, a rear end bearing 12, and a main head bearing 13, the bearings being fixedly secured to the bottom plate in any suitable manner. The bearing 12 mounts a clamping bar 14, which is secured in place by machine screws 15, the members 12 and 14 being suitably conformed to receive parallel guide rods 16, 17, in sliding bearing engagement. The main head bearing 13 is provided with aligned apertures orv journals 18, which also receive the guide rods in sliding bearing engagement. The bearing 13 is further provided with a master thread nut-receiving aperture 19.

The work holder 20 comprises a tailstock center bearing 21 mounting a tailstock 22, and provided with slotted side bearings clamped in place on the guide rods by machine screws 23. A thrust arm 24, having slotted side bearings 25, is clamped in place on the guide rods by machine screws 26. The arm 24 is further provided with a central transverse groove or saddle 27 adapted to freely receive theshank 33 of a master thread unit spindle 30. The members 21 and 24 are fixedly secured, in spaced relation, on the guide rods 16, 17, and form a reciprocable unit therewith, which unit is reciprocable in the fixture base in accordance with a suitable movement of the master thread unit spindle 30 in a master thread unit nut 40 which is locked in place in bearing 13 by a set screw 41. The spindle 30 comprises a threaded body portion 31, reduced at both ends to form a headstock 32 and a shank 33, which shank is further reduced to form a partially threaded tail piece 34 to which is secured a driving handle or crank 35. Suitable lock nuts 36 are threaded up on the tail piece and serve to hold the shouldered end of the threaded body portion 31 abutted against the thrust arm 24 when the unit is in use. A driving plate 38 is fitted over the headstock 32 and mounts a work driving dog 39 which is secured to work piece 42 by set screw 43. The work piece is mounted on axial centers between the headstock and the tail-stock, and in the horizontal plane of the guide rods, as shown. The work piece is provided with a reduced portion 44, to be threaded, which portion is reciprocated, by the crank handle 35, in the path of grinding wheel 45 mounted on a spindle 46. The unit 10 and attachments are mounted on magnetic chuck 47 of a suitable surface grinder, not shown.

It will be seen that the device of the present invention insures the utmost accuracy in thread grinding, which accuracy is obtained, inter alia, by using a rather large diameter master screw to secure the maximum amount of bearing area, and by positioning the guide rods 16 and 17,. together with the thrust member 24, on the same center line as the work piece, whereby the possibility of deflection, misalignment, and play in the work piece is substantially eliminated.

In the operation of the device, the work piece is suitably prepared and mounted between the stocks, a master thread unit of suitable thread pitch having been previously mounted in place. The master thread unit is clamped to the thrust arm by the lock nuts 36, whereby the work piece is fixedly held between its centers, The work driving dog and driving plate are secured, and the unit is ready for the apposition of the reduced shank of the work piece to the grinding wheel. oriented, the device is fixedly held in 'place by passing current through the magnetic chuck, or clamping a me chanical chuck in place, where one is used. Upon turning the crank handle, the work piece carrier 20 is advanced and the work piece rotated on its axis. As the portion of the work piece which is to be threaded is brought into engagement with the grinding wheel in an advancing helix corresponding to the master-thread, a

With all parts properlythread of corresponding pitch is ground in the work piece. To grind screws of varying pitches, all that is necessary is a master thread unit and nut for each thread or pitch, these units being replaceable by loosening set screw 41 and lock nuts 36, whereby the thread unit can be removed and a replacement inserted. The novel device, with thread units of difierent pitches, is small, easily handled by one man, and can be stored without difficulty. The simplicity of construction of the device enables it to be easily set-up and operated as a screw thread grinding accessory for a surface grinder.

There has been described and illustrated a device capable of performing all of the specifically mentioned objects of this invention as well as others which are apparent to those skilled in the art. Various uses of the present invention may be made employing the described structure. Accordingly, it is apparent that variations as to operation, size and shape, and rearrangement of elements may be made without departing from the spirit of the invention. Accordingly, limitation is sought only in accordance with the scope of the following claims.

What is claimed is:

1. A screw thread grinding attachment for use with a surface grinding machine having a magnetic chuck, comprising, in combination, a work holder adapted to be magnetically held by the chuck, said work holder comprising a U-shaped base member having upstanding end lugs mounting spaced, parallel guide rods, a. pair of guide rods reciprocably mounted in said end lugs, a master thread nut demountably secured to the base, work engaging means fixedly secured to the guide rods and reciprocable therewith, said work engaging means including a workholding chuck, said work engaging means having its axis lying in the horizontal plane of the axes of the guide rods, a master spindle having threaded engagement with the master thread nut, and fixedly secured to the work-holding chuck, and crank means for the spindle, whereby the spindle and its associated work-piece can be advanced in the work holder in accordance with the pitch of the master thread spindle.

2. A screw thread grinding attachment for use with surface grinding machines, comprising, in combination, a base member having a fiat bottom apposable to the bed of a surface grinder, and upstanding end lugs slidably mounting spaced, parallel guide rods; a master thread nut demountably secured in said base; work engaging means fixedly secured to said guide rods and reciprocable therewith, said work engaging means including a workholding chuck; a master spindle threadedly engaging the master thread nut, and fixedly secured to said work-holding chuck; and a crank handle for the master spindle, whereby the work engaging means is reciprocated along the base member when the crank is turned.

3. In a screw thread grinding attachment of the character described, a work holder comprising a base member having a pair of spaced parallel guide rods reciprocably mounted thereon, work engaging means fixedly secured to the guide rods and reciprocable therewith, said work engaging means including a work-holding chuck, a master thread nut demountably secured to the work holder base, a master spindle having threaded engagement with the master thread nut, and fixedly secured to the work-holding chuck, and crank means for the spindle, whereby the spindle and an associated work-piece can be advanced in the work holder in accordance with the pitch of the master thread spindle.

References Cited in the file of this patent UNITED STATES PATENTS 

